1. Technical Field
Improved dual rocking piston and diaphragm compressors as well as vacuum pumps are disclosed. More specifically, improved dual piston assemblies for use in rocking piston compressors, diaphragm compressors and vacuum pumps are disclosed. In one embodiment, improved balance is achieved by providing pistons with equal stroke lengths, piston heads and retainers with unequal diameters and piston assemblies with equal masses so that the moments of inertia and centers of gravity of each piston assembly are diametrically opposite the drive shaft from one another and cancel each other out for improved balance. In another embodiment, piston assemblies of different stroke lengths are used, and the forces of each piston assembly cancel each other out by adjusting the masses of the various components in consideration of the acceleration of each piston assembly.
2. Description of the Related Art
Dual rocking piston compressors, diaphragm compressors and vacuum pumps all use the reciprocating motion of a piston to produce increased pressures within a control volume, such as a cylinder. The length of the stroke of the piston determines the compression ratio for the fixed control volume. Dual rocking pumps are often used for medical applications, such as used in oxygen concentrators, because they are compact. Because a pump used in a medical application needs to be quiet for the comfort of the patient, it is important to reduce any vibration during operation of the pump.
One problem with conventional dual rocking piston pumps is that they can create noise and vibration as the pistons reciprocally stroke, especially if the two pistons are designed for different outputs, thereby leading to improper balancing. If each piston assembly produces a different output, different rod top/retainer/diaphragm diameters, forces of different magnitudes are imposed on the drive shaft by each piston assembly. Shaking or vibrations arise as the drive shaft rotates because of the imbalance in the forces imposed by each piston assembly.
Further, it is often desirable to design dual rocking piston pumps with unequal piston strokes. A dual opposed rocking piston pump with unequal strokes is also inherently out of balance. Because the strokes are different, the opposed reciprocating piston assemblies are traveling different distances during each revolution. As a result, the acceleration of one piston assembly is not equal to the acceleration of the other piston assembly. The diameters of the retainers, rod tops or diaphragms may or may not be equal and the mass of the opposed reciprocating components may or may not be equal. The force created by each reciprocating components is a function of mass and acceleration (Force=Mass·Acceleration). If the product of the mass and acceleration of the opposed reciprocating components is not equal a shaking or vibrating force will be created resulting in unwanted noise and vibration.
As a result, there is a need for an improved rocking piston pump or compressor with improved balance and quieter operation without requiring identical piston assemblies or identical output of the piston assemblies.